Alkylated naphthalenes as synthetic lubricant base stocks

ABSTRACT

This invention relates to alkylated methylnaphthalenes and their utility in lubricant base stocks. In particular, the alkylated methylnaphthalenes of the present invention have unexpectedly superior thermal and oxidative properties and may be used to improve the performance characteristics of other lubricant base oils.

FIELD OF THE INVENTION

[0001] This invention relates to alkylated methylnaphthalenes and theirutility in synthetic lubricant base stocks.

BACKGROUND OF THE INVENTION

[0002] Alkylaromatic fluids have been proposed for use as certain typesof functional fluids where good thermal and oxidative properties arerequired. For example, U.S. Pat. No. 4,714,794 (Yoshida) describesmonoalkylated naphthalenes as having excellent thermal and oxidativestability, low vapor pressure and flash point, good fluidity and highheat transfer capacity and other properties which render them suitablefor use as thermal medium oils. The use of a mixture of monoalkylatedand polyalkylated naphthalenes as a base for synthetic functional fluidsis described in U.S. Pat. No. 4,604,491 (Dressler). Pellegrini U.S. Pat.Nos. 4,211,665 and 4,238,343 describe the use of alkylaromatics astransformer oils.

[0003] The alkylated naphthalenes are usually produced by the alkylationof naphthalene or a substituted naphthalene in the presence of an acidicalkylation catalyst such as a Friedel-Crafts catalyst, for example, anacidic clay as described in Yoshida U.S. Pat. No. 4,714,794 or DresslerU.S. Pat. No. 4,604,491 or a Lewis acid such as aluminum trichloride asdescribed in Pellegrini U.S. Pat. Nos. 4,211,665 and 4,238,343. The useof a catalyst described as a collapsed silica-alumina zeolite for thealkylation of aromatics such as naphthalene is disclosed in Boucher,U.S. Pat. No. 4,570,027. The use of various zeolites includingintermediate pore size zeolites such as ZSM-5 and large pore sizezeolites such as zeolite L and ZSM-4 for the alkylation of variousmonocyclic aromatics such as benzene is disclosed in Young, U.S. Pat.No. 4,301,316.

[0004] In the formulation of functional fluids based on the alkylnaphthalenes, it has been found that the preferred alkyl naphthalenesare the mono-substituted naphthalenes since they provide the bestcombination of properties in the finished product. The mono-substitutednaphthalenes possess fewer benzylic hydrogens than the correspondingdi-substituted or polysubstituted versions and were said to have betteroxidative stability and therefore form better functional fluids andadditives. In addition, the mono-substituted naphthalenes have akinematic viscosity in the desirable range of about 5-8 cSt (at 100° C.)when working with alkyl substituents of about 14 to 18 carbon atomschain length. Numerous work has been done to improve the selectivity tothe desired mono-alkylated naphthalenes:

[0005] U.S. Pat. No. 5,034,563, Ashjian et al., which is incorporated byreference, teaches use of a zeolite containing a bulky cation. The useof, e.g., USY with cations having a radius of at least about 2.5Angstroms increases selectivity for desired mono-alkylated products.Suitable zeolites include those containing hydrated cations of metals ofGroup IA, divalent cations, especially of Group IIA, and cations of theRare Earths.

[0006] U.S. Pat. No. 5,177,284, Le et al., which is incorporated byreference, discusses the desirable properties of alkylated naphthalenefluids with higher alpha:beta ratios, including improved thermal andoxidative stability. Le et al. found that several parameters influencedthe alpha:beta ratio of the alkylated naphthalene products, includingsteaming the zeolite, lowering the alkylation temperature, or using anacid-treated clay.

[0007] U.S. Pat. No. 5,191,135 Dwyer et al., which is incorporated byreference, discloses the effect of co-feeding water for the alkylationreaction when using a large pore zeolite catalyst, such as zeolite Y.U.S. Pat. Nos. 5,191,134, and 5,457,254, incorporated by referenceherein, disclose a similar alkylation process using MCM-41 and a mixedH/NH₄ catalyst, respectively.

[0008] As previously noted, the prior art taught that mono-substitutednaphthalene is the most desirable component for synthetic lubricant basestock with optimized thermal and oxidative stability and viscometrics.Accordingly, the prior art taught processes to improve selectivity andachieve the desired mono-alkylated products. Di-alkyl naphthalenes werethought to have inferior lubricant properties because di-alkylationinhibits the naphthalene rings to neutralize the oxygen, peroxides orradicals. Alkylated naphthalenes with di- or tri-alkyl components werethought to have poor thermal and oxidative stabilities.

SUMMARY OF THE INVENTION

[0009] It has now been discovered that di-, tri-, or tetra-alkylnaphthalenes, in particular alkyl methylnaphthalenes, contrary to theteachings of the art, have superior thermal and oxidative properties, inmany cases significantly better than mono-substituted naphthalenes.

[0010] Accordingly, the present invention extends the range of rawmaterials that can be used to produce synthetic base stock andestablishes that alkyl methylnaphthalenes have better oxidativestability than known alkyl naphthalene fluid.

[0011] The present invention includes di-, tri- or tetra-alkylnaphthalenes, preferably di-alkyl naphthalenes, as having utility assynthetic lubricant base stocks, blending stocks, or as additives forother base stock fluids or liquid fuels. The present invention includesa base oil comprising a mixture of monoalkylated and polyalkylatednaphthalenes wherein the improvement comprises said base oil containingat least 20 wt % of an alkylated naphthalene selected from the groupconsisting of a compound or mixture of compounds of the followingformula (I):

[0012] wherein R¹ and R² are H, methyl, ethyl, n-propyl, n-butyl, ort-butyl;

[0013] R³ and R⁴ are an alkyl group having from about 6 to about 24carbon atoms;

[0014] x is from 0 to about 2; and

[0015] y is from 0 to about 4;

[0016] with the proviso that at least one of R¹ and R² is other than H,and at least one of x and y is other than 0.

[0017] Preferably only one of R¹ and R² is alkyl and the other H, mostpreferably one of R¹ and R² is H and the other is methyl.

[0018] The compounds of formula (I) have unexpectedly superior thermaland oxidative properties, especially when compared to mono-substitutednaphthalenes. The term mono-substituted naphthalenes, as used herein,generally refers to naphthalene having a single substitution, such as analkyl group having from about 6 to about 24 carbon atoms.

[0019] Another aspect of the present invention is directed to a methodfor improving the oxidative stability of lubricants comprising adding tothe lubricant a base oil comprising a compound of formula (I).

[0020] Hence the method is directed to a method for improving theoxidative stability of a lubricant having an RBOT of ≦about 200 minutescomprising adding to said lubricant a base oil comprising a compound offormula (I):

[0021] wherein R¹ and R² are H, methyl, ethyl, propyl, or butyl;

[0022] R³ and R⁴ are an alkyl group having from about 6 to about 24carbon atoms;

[0023] x is from 0 to about 2; and

[0024] y is from 0 to about 4;

[0025] with the proviso that at least one of R¹ and R² is other than H,and at least one of x and y is other than 0;

[0026] and wherein the base oil has a RBOT value of greater than about200 minutes.

DETAILED DESCRIPTION OF THE INVENTION

[0027] As used herein, “alkylated methylnaphthalene” refers to anaphthalene compound that has a methyl group at the one or two positionof the naphthalene ring and at least one additional alkyl groupcontaining about 6 carbon atoms to about 24 attached at another positionof the ring. In addition, all values set forth herein include allcombinations and sub-combinations of ranges and specific values giventherein.

[0028] The starting materials for the production of compounds of formula(I) are substituted naphthalenes which may contain one or more shortchain alkyl groups containing up to about eight carbon atoms, such as amethyl, ethyl, propyl, or butyl group. Preferably, the starting materialcomprises 1-methylnaphthalene, 2-methylnaphthalene or a mixture of thetwo in any proportion. For example, 1- and 2-methylnaphthalenes arepresent in coke liquids or in the heavy fraction (greater than 10 carbonatoms) of aromatic reformate streams or the heavy bottom stream from atoluene disproportionation process or the heavy fraction from acatalytic cracking process, such as light cycle oil from an FCC process.Feed streams with higher 2-methylnaphthalene content, such as those fromthe highly selective toluene disproportionation process, are preferablebecause the alkylated 2-methylnaphthalene products generally have betteroxidative stability and the alkylation process tends to be moreefficient when compared to feedstreams containing higher amounts of1-methylnaphthalenes. Additionally, the starting material may comprise amixture of methylnaphthalene and naphthalene.

[0029] The alkylating agents which may be used to alkylate thesubstituted naphthalenes include any aliphatic or aromatic organiccompound having one or more available alkylating aliphatic groupscapable of alkylating the substituted naphthalene. The alkylatable groupitself should have at least about 6 carbon atoms, preferably at leastabout 8, and still more preferably at least about 12 carbon atoms. Forthe production of functional fluids and additives, the alkyl groups onthe naphthalene preferably have from about 12 to about 24 carbon atoms,with particular preference to about 14 to 18 carbon atoms. A preferredclass of alkylating agents are the olefins with the requisite number ofcarbon atoms, for example, the dodecenes, tetradecenes, pentadecenes,hexadecenes, heptadecenes, octadecenes, nonadecenes, and their branchedanalogs.

[0030] In preferred embodiments, the alkylating agent will be an olefinwhich may include internal olefins (such as 2- or 3-tetradecene), alpha(or 1-) olefins, vinylidene olefins (such as 2-methyl-1-tetradecene or2,3,3-trimethyl-1-butene, or 2,4,4-trimethyl-1-pentene, or2,4,4-trimethyl-2-pentenes). The alpha olefins and linear internalolefins are most readily available.

[0031] Mixtures of olefins, for example, mixtures of C₁₂-C₂₀ or C₁₄-C₁₈olefins, may also be used in the present invention. Branched alkylatingagents, especially oligomerized olefins such as the trimers, tetramers,or pentamers of light olefins such as ethylene, propylene, and butylenesare also useful. Other useful alkylating agents which may be used,include alcohols such as hexadecanols, heptadecanols, octadecanols,nonadecanols, dodecanols and doundecanols. Alkyl halides such ashexadecyl chlorides, octadecyl chlorides, dodecanyl chlorides, andhigher homologs may also be used in the present invention.

[0032] Previous prior art references relating to production ofalkylnaphthalenes emphasized making high amounts of mono-alkylnaphthalenes. In the present invention, di-alkyl naphthalene (e.g.methyl at the 1 or 2 position and an alkyl group of about 6 carbon atomsattached at another position of the ring) may be consistently producedbecause one of the alkyl groups is a small alkyl substituent, such asmethyl or ethyl. The di-alkyl product may be achieved by carefullyselecting the starting material and by controlling the first alkyl grouppresent in the naphthalene ring.

[0033] The alkylation reaction between the substituted naphthalene andthe alkylating agent is carried out in the presence of an alkylationcatalyst. Typically, the catalyst comprises a zeolite catalyst whichcontains a cation of certain specified radius. The molecular size of thealkylation products will require a relatively large pore size in thezeolite in order for the products to leave the zeolite, which will alsotend to reduce diffusion limitations with the long chain alkylatingagents. The large pore size zeolites are the most useful zeolitecatalysts for this purpose although the less highly constrainedintermediate pore size zeolites may also be used, as discussed below.Acidic clay materials such as Fitrol 20, 22, and 24 from Englehard Co.are also useful.

[0034] Large pore size zeolites include faujasite, the syntheticfaujasites (zeolites X and Y), zeolite L, ZSM-4, ZSM-18, ZSM-20,mordenite and offretite. Such zeolites are characterized by the presenceof a 12-membered oxygen ring system in the molecular structure and bythe existence of pores with a minimum dimension of at least 7.4Angstrom, as described by Frilette et al. in J. Catalysis 67, 218-222(1981). See also, Chen et al., Shape-Selective Catalysis in IndustrialApplications, Chemical industries, vol. 36, Marcel Dekker Inc., New York1989, ISBN 0-8247-7856-1 and Hoelderich et al. Angew. Chem. Int. Ed.Engl., 27, 226-246 (1988), pp.226-229. The large pore size zeolites mayalso be characterized by a “Constraint Index” (CI) of not more than 2,in most cases not more than 1. The method for determining CI isdescribed in U.S. Pat. No. 4,016,218, together with values for typicalzeolites. The significance of the Index is described in U.S. Pat. No.4,861,932, to which reference is made for a description of the testprocedure and its interpretation.

[0035] Zeolites whose structure is that of a ten membered oxygen ring,generally regarded as the intermediate pore size zeolites, may also beeffective catalysts for this alkylation reaction if their structure isnot too highly constrained. Zeolites such as ZSM-12 (CI 2) may beeffective catalysts for the alkylation reaction. The zeolite identifiedas MCM-22 is also a useful catalyst for this reaction and is describedin U.S. Pat. No. 4,954,325 incorporated herein by reference. Inaddition, MCM-56, described in U.S. Pat. No. 5,362,697, incorporatedherein by reference, may also be used. Zeolites having a CI up to about3 will generally be useful catalysts, although the activity may be foundto be dependent on the choice of alkylating agent, especially its chainlength, a factor which imposes diffusion limitations upon the choice ofzeolite. Other useful catalysts include MCM-49, described in U.S. Pat.Nos. 5,236,575 and 5,371,310, incorporated herein by reference.

[0036] Another useful zeolite in accordance with the present inventionincludes ultrastable Y, usually referred to as USY. When this materialcontains hydrated cations, it catalyzes the alkylation in good yieldswith excellent selectivity. Zeolite USY is a material of commerce,available in large quantities as a catalyst for the cracking ofpetroleum. It is produced by the stabilization of zeolite Y by aprocedure of repeated ammonium exchange and controlled steaming.Processes for the production of zeolite USY are described in U.S. Pat.No. 3,402,966 (McDaniel), U.S. Pat. No. 3,923,192 (Maher) and U.S. Pat.No. 3,449,070 (McDaniel); see also Wojciechowski, Catalytic Cracking,Catalysts, Chemistry and Kinetics, Chemical Industries, vol. 25, MarcelDekker, New York, 1986, ISBN 0-8247-7503-8, to which reference is madefor a description of zeolite USY, its preparation and properties.

[0037] The most preferred zeolites in accordance with the presentinvention include USY, MCM-22, MCM-49 and MCM-56.

[0038] Additionally, other catalysts that may be used in the presentinvention include a zeolite having both ammonium and protonic speciesassociated with the exchangeable sites of the zeolite. Such a catalystis disclosed in U.S. Pat. No. 5,457,254, Artdito et al., incorporatedherein by reference. As also disclosed in U.S. Pat. No. 5,457,254,selected zeolite catalysts preferably contain a limited amount of one ormore of the Rare Earths.

[0039] The catalyst of the present invention may be composited with amatrix material or binder which is resistant to the temperatures andother conditions employed in the alkylation process. Such materialsinclude active and inactive materials and synthetic or naturallyoccurring zeolites as well as inorganic materials such as clays, silicaor silica-alumina. The latter may be either naturally occurring or inthe form of gelatinous precipitates or gel including mixtures of silicaand metal oxides. Use of an active material in conjunction with thezeolite may change the conversion and/or selectivity of the catalyst.Inactive materials suitably serve as diluents to control the amount ofconversion so that alkylation products can be obtained economically andorderly without employing other means for controlling the rate ofreaction. Binders which may be incorporated to improve the crushstrength and other physical properties of the catalyst under commercialalkylation operating conditions include, but are not limited to,naturally occurring clays, e.g., bentonite and kaolin, as well assilica, alumina, zirconia and mixtures thereof.

[0040] The alpha value of the zeolite is an approximate indication ofthe catalytic cracking activity of the catalyst compared to a standardcatalyst. The alpha test gives the relative rate constant (rate ofnormal hexane conversion per volume of catalyst per unit time) of thetest catalyst relative to the standard catalyst which is taken as analpha of 1 (Rate Constant=0.016 sec −1). The alpha test in described inU.S. Pat. No. 3,354,078 and in J. Catalysis, 4, 527 (1965); 6, 278(1966); and 61, 395 (1980), to which reference is made for a descriptionof the test.

[0041] Generally, zeolites with high alpha values ranging from about 10to about 1000 are preferred for use in the present invention. Mostcatalysts have alpha values greater than 30 and some zeolites, such as Yand USY have high initial alpha values up to about 1000. For purposes ofthe present invention, alpha values from about 10 and higher areeffective in the alkylation process. MCM-22, MCM-49 and MCM-56 generallyhave stable and high alpha values from about 40 to about 500 and areespecially suitable for fixed-bed continuous operations.

[0042] The stability of the alkylation catalyst of the invention may beincreased by steaming. U.S. Pat. Nos. 4,663,492; 4,594,146; 4,522,929;and 4,429,176 are incorporated by reference herein, and describeconditions for the steam stabilization of zeolite catalysts which can beutilized to steam-stabilize the catalyst.

[0043] The alkylation process of this invention is conducted such thatthe organic reactants, e.g., the alkylatable methylnaphthalene compoundand the alkylating agent, are brought into contact with the catalyst ina suitable reaction zone such as, for example, in a flow reactorcontaining a fixed bed of the catalyst composition, under effectivealkylation conditions. The preferred starting material,methylnaphthalene, will be used in describing the alkylation conditions.

[0044] Alkylation reaction conditions typically include a temperature offrom about 100° C. to about 400° C., preferably from about 150° C. toabout 250° C. Generally, reaction rates may be too slow below 100° C.,and temperatures above 300° C. may promote undesirable side reactionsthat may degrade product properties and yield.

[0045] Typical reaction pressures include a pressure from about 0.1 toabout 100 atmospheres, preferably from about 1 to about 30 atmospheres.The required pressure may be maintained by inert gas pressurization,preferably with nitrogen.

[0046] Typical reaction times are from about 0.5 to about 100 hours,preferably from about 2 to about 30 hours. The reaction time isdependent on temperature and the amount of catalyst used in the process.Generally, higher reaction temperatures and a higher catalyst chargepromotes faster reaction rates.

[0047] Typical alkylatable methylnaphthalene compound to alkylatingagent mole ratio (MN:O) is from about 1:3 to about 10:1, preferably fromabout 1:2 to about 3:1.

[0048] Generally, the amount of catalyst charged is about 0.1 wt % toabout 10 wt % in a slurry reactor. A low catalyst charge may causelonger reaction times and a high catalyst charge may be uneconomical torun, causing filter plugging during the catalyst removal step.Preferably, the catalyst charge is about 0.5 wt % to about 5 wt %. Thereaction may be carried out in a fixed-bed continuous operation wherethe catalyst is in pellet or extruded form and packed in a tubularreactor heated to a desirable temperature. The feed is introduced at aspecific weight hourly space velocity (WHSV) ranging from about 0.1 toabout 20, preferably from about 0.5 to about 5, to achieve a highconversion.

[0049] Preferred reaction conditions include a temperature within theapproximate range of from about 150 to about 250° C., a pressure of fromabout 1 to about 30 atmospheres, a reaction time of from about 2 toabout 30 hours, and an MN:O mole ratio of from about 1:2 to about 3:1,with a preferred catalyst charge from about 1 wt % to about 5 wt % in aslurry reactor, or a WHSV of about 0.2 to about 4 in a fixed bedcontinuous operation.

[0050] The reactants can be in either the vapor phase or the liquidphase and can be neat, i.e., free from intentional admixture or dilutionwith other material, or they can be brought into contact with thecatalyst composition with the aid of carrier gases or diluents such as,for example, hydrogen or nitrogen. The alkylation can be carried out asa batch-type reaction typically employing a closed, pressurized, stirredreactor with an inert gas blanketing system or in a semi-continuous orcontinuous operation utilizing a fixed or moving bed catalyst system.

[0051] In preparing compounds of formula (I), an amount of dimer of thealkylating olefin will be co-produced. The basestocks herein comprisingformula (I) will typically contain <1 wt % dimer whether used as abasestock or as a co-basestock.

[0052] The compounds of formula (I) are characterized by exceptionaloxidative and thermal stability. They may be separated from the reactionmixture by stripping off unreacted alkylating agent and the formula (I)compound in the conventional manner. It has also been found that thestability of the alkylated product may be improved by filtration overactivated charcoal and by alkali treatment to remove impurities,especially acidic by-products formed by oxidation during the course ofthe reaction. The alkali treatment is preferably carried out byfiltration over a solid alkali material, preferably calcium carbonate(lime).

[0053] The synthetic lubricant base stocks of the present invention

[0054] comprise compounds represented by the following general formula(I):

[0055] wherein R¹ and R² are H, methyl, ethyl, propyl, or butyl;

[0056] R³ and R⁴ are an alkyl group having from about 6 to about 24carbon atoms;

[0057] x is from 0 to about 2; and

[0058] y is from 0 to about 4;

[0059] with the proviso that at least one of R¹ and R² is other than H,and at least one of x and y is other than 0.

[0060] In preferred embodiments, either R¹ or R² is H and the otheralkyl, most preferably either R¹ or R² is H and the other is methyl.Accordingly, 1- or 2-methylnaphthalenes or mixtures thereof arepreferred starting materials. Generally, mixtures high in2-methylnaphthalenes are more preferred because they may be morereactive than 1-methylnaphthalenes and the 2-methylnaphthalenealkylation product has better stability than 1-methylnaphthalenealkylation products. As noted previously, the heavy bottom stream fromhighly shape-selective toluene disproportionation processes aretypically high in 2-methylnaphthalenes and especially suitable for usein the present invention.

[0061] Also, in preferred embodiments, R³ and R⁴ comprise alkyl groupshaving from about 6 to about 24 carbon atoms, more preferably, fromabout 8 to about 18 carbon atoms. Exemplary R³ and R⁴ groups includehexyl, heptyl, octyl, nonyl, iso-octyl, 2-ethyl hexyl, decyl, undecyl,dodecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, and octadecyl,each optionally having linear or branched alkyl groups.

[0062] The sum of x and y is preferably from about 1 to about 3. Morepreferably, the synthetic oils comprise di-alkyl naphthalenes whereinthe sum of x and y is one, R¹ is H and R² is methyl. The synthetic oilsmay comprise higher-alkylated naphthalenes wherein the sum of x and y isgreater than one, or from about 2 to about 3. Where mixtures ofcompounds of formula (I) are used, the ratio of di-alkyl naphthalenes totri- or tetra-alkyl naphthalenes may be from about 3 to about 1, morepreferably from about 25 to about 1. The amount of di-alkyl naphthaleneproduct versus tri- or tetra-alkyl naphthalene product may be controlledby changing the methylnaphthalene to alkylating agent olefin ratio inthe feed, catalyst type and/or reaction temperature. Usually, a lowermethylnaphthalene to olefin ratio (higher olefin content) favors theformation of tri- or tetra-alkylated naphthalenes.

[0063] The compounds of formula (I) described herein exhibit excellentthermal and oxidative properties which make them particularly suitablefor use in lubricant base oils. Such properties have generally beensuperior and unexpected, particularly when compared to mono-substitutednaphthalenes. The compounds of formula (I) may be characterized, forexample, by oxidation stability, viscosity, and pour point. Generallyspeaking, the thermal and oxidative properties of the compounds offormula (I) may vary depending on the alkylating conditions including,for example, the starting material to alkylating agent ratio, thereaction temperature, and the particular alkylating agent used.

[0064] The compounds of formula (I) may be used to improve the oxidativestability of lubricants. For example, the oxidation stability of thecompounds of formula (I) as measured under the Rotating Bomb OxidationTest (RBOT) (ASTM D2272) is generally greater than about 200 minutes,more preferably greater than 500 minutes. In preferred embodiments, theRBOT values are from about 500 to 1500 minutes, more preferably between700 and 1200 minutes. All values set forth herein include allcombinations and subcombinations of ranges and specific values giventherein.

[0065] In addition, the kinematic viscosity of the compounds of formula(I) at 100° C. is from about 2 to about 30 cS, more preferably fromabout 3 to about 20 cS, with viscosity index (VI) values from about 50to about 180, preferably greater than 60. The pour point of thecompounds of formula (I) is from about 0 to about −60° C., morepreferably from −10 to about −55° C. All values set forth herein includeall combinations and sub-combinations of ranges and specific valuesgiven therein.

[0066] Typically, the base oils of the present invention which comprisebasestocks of formula (I) comprise about 20 wt % of a compound offormula (I) or mixtures thereof and preferably greater than about 50 wt% of a compound of formula (I) or mixtures thereof. Such amounts maydepend on the particular application and/or the performancecharacteristics desired. The base oils of the present invention haveRBOT of at least about 200.

[0067] The synthetic base oils comprising compounds of formula (I) maybe used by themselves as the basestock for synthetic lubricantformulations. They can also be used as a co-base stock with othersynthetic basestocks, such as polyalphaolefins (PAO), polyalkyleneglycol(PAG), polybutene (PIB), alkylbenzene (AB), or with conventional mineraloils, such as 100 to 800 SUS SN oils from catalytic or conventionaldewaxed processes. The base oils comprising compounds of formula (I) mayalso be used with hydrocracked or hydroisomerized basestocks such asUCBO from Chevron, BP hydrocracked stocks, slack wax-isomerizedbasestocks or Fischer-Tropsh wax-isomerized basestocks (collectively,these fluids are referred to as Group II and Group III basestocks). Theabove basestocks typically have RBOT of ≦ about 150.

[0068] Generally, when used as a co-basestock, the base oil of thepresent invention comprises from about 2 to about 60 wt % of the totallubricant basestock, and preferably greater than about 5 wt % of thetotal lubricant basestock. The use of the base oils of the presentinvention significantly improves the finished lubricant's thermal,oxidative, and hydrolytic stability as well as lubricant additivesolvency, sludge dispersancy and antiwear or extreme-pressure metalsurface protection.

[0069] As noted above and indicated in the following examples, compoundsof formula (I) have superior oxidative stabilities and viscometrics whencompared to mono-alkylated naphthalenes. Accordingly, the synthetic baseoils of the present invention may be substantially devoid ofmono-alkylated naphthalenes and still provide excellent lubricatingproperties.

[0070] The base oils of the present invention may be incorporated withconventionally used additives for lubricating oils such as anantioxidant, detergent dispersant, viscosity index improver, pour pointdepressant, oiliness improver, anti-wear agent, extreme pressure agent,friction modifying additive, anti-corrosive agent, metal inactivatingagent, anti-rust agent, seal compatibility improver, anti-foaming agent,emulsifier, demulsifier, bactericide, or colorant.

[0071] The base oils of the present invention may be used to lubricatesurfaces of various structures and elements that require lubrication. Asused herein, “surface” refers to the outer part of structures orparticles. The compounds of formula (I) may be used in variousfunctional fluid formulations such as crank case lubricant, two cycleengine oil, hydraulic lubricant, drilling lubricant, turbine oil,grease, gear oil, transmission oil, and paper machine oil.

[0072] The following examples are illustrative and not meant to belimitations.

EXAMPLES

[0073] The general procedure described herein was used to collect thefollowing data and is specifically described for Example 2 of Table 1.In this experiment, 1-methylnaphthalene (1-MN), 142 gram (1 mole) and12.5 gram USY catalyst were premixed in a 500 ml round bottom flask andthe complete reaction system was purged with N₂ to eliminate air. Thereaction flask was heated to 200° C. under nitrogen atmosphere.1-hexadecene, 112 gram (0.5 mole), was added slowly into this mixture intwo hours. The reaction mixture was reacted for three more hours andthen cooled down to room temperature. Analysis of the reaction mixtureby gas chromatography was used to determine the amounts of unreactedreactants and showed that most of the C₁₆ olefin was converted intoproduct. The product, i.e. the lube product, was isolated by filteringoff the solid catalyst and distilled at 120° C./<1 millitorr vacuum formore than one hour to remove any unreacted olefin and methylnaphthalene(MN).

[0074] The resulting product was analyzed and product properties aresummarized below. Oxidation stability was analyzed under the RotatingBomb Oxidation Test (RBOT) and the B-10 oxidation test. The RBOT testprotocol is described in ASTM D2272.

[0075] The B-10 oxidation test is used to evaluate mineral oil andsynthetic lubricants either with or without additives. The evaluation isbased on the resistance of the lubricant to oxidation by air underspecified conditions as measured by the formation of sludge, thecorrosion of a lead specimen, and changes in neutralization number andviscosity. In this method, the sample is placed in a glass oxidationcell together with iron, copper and aluminum catalysts and a weighedlead corrosion specimen. The cell and its contents are placed in a bathmaintained at a specified temperature and a measured volume of dried airis bubbled through the sample for the duration of the test. The cell isremoved from the bath and the catalyst assembly is removed from thecell. The oil is examined for the presence of sludge, the total acidnumber (TAN) (ASTM 664), and Kinematic Viscosity (Kv) increase at 100°C. (ASTM D445). The lead specimen is cleaned and weighed to determinethe loss in weight.

[0076] Other properties to be measured include Bromine No. (ASTM D1159),VI, and Pour Point (ASTM D97).

[0077] The following examples illustrate the excellent thermal andoxidative stabilities of the compounds of formula (I) as well as theeffect of several variables on the properties and yield of thecompounds, i.e., lube products.

[0078] The data in Table 1 demonstrates the effect of MN/olefin molarratios on the lube product (a methylnaphthalene acts as the startingmaterial and an olefin acts as the alkylating agent for purposes of theexamples herein). Examples 1 to 3 show that increasing 1-MN/olefin molarratios from 1/1 to 4/1 improves the oxidative stability of the lubeproduct as measured by RBOT (the RBOT time increases from 145 minutes to805 minutes). A similar trend was observed for 2-MN/olefin molar ratios(Examples 4 and 5). Varying the MN/olefin ratios do not appear to changeproduct viscosities, VI, and pour points and conversion of olefins werevery high (>90%) at all MN/olefin ratios. TABLE 1 Effect of MN/OlefinMolar Ratio Example No. 1 2 3 4 5 Feed, MN 1-MN 1-MN 1-MN 2-MN 2-MNOlefin C16 1-C16 C16 1-C16 1-C16 Mole Ratio MN/O 1/1 2/1 4/1 1.0/1 2.0/1Catalyst Type USY USY USY USY USY Catalyst Wt % 5 5 5 5 5 Rxn Temp, ° C.200 200 200 200 200 Rxn Time, Hrs. 18 4 4 9 18 % Total Conv. 94.5 71.358.0 95.3 77.9 % 1-C16 Conv. 94.2 95.9 98.5 95.7 97.7 ProductSelectivity mono-C16-MN 95.6 94.1 99.6 96.1 99.7 di-C16-MN 4.4 2.8 0.43.9 0.3 others 0.0 3.1 0.0 0.0 0.0 Product Properties Kv @ 100° C., cS5.7 5.6 5.8 5.5 5.3 Kv @ 40° C., cS 41.4 41.0 40.9 38.4 36.8 VI 67 62 7667 64 Pour Point, ° C. −47 −46 −46 −48 −49 Bromine No. 0.27 0.5 0.450.02 0.03 Oxidative Stability RBOT, min 145 703 805 239 744 B10 Test at163° C./40 hrs % Kv Increase 21.8 6.5 0.0 12.0 10.2 TAN Incr., mg 1.871.6 0.35 0.9 1.1 KOH Sludge nil nil trace light trace wt % lead loss19.5 7.2 2.6 10.1 8.6

[0079] The data in Table 2 demonstrates the effect of reactiontemperature on lube yields and properties from 1-MN or 2-MN at a 2/1MN/olefin mole ratio. Examples 6 to 8 show that increasing reactiontemperature from 175 to 225° C. increases 1-hexadecene conversion from74% to 100%, but this has no effect on viscosities, VI and pour points.At lower reaction temperatures, such as 175° C. and 200° C. (Ex. 6 and7), the lube products have longer RBOT time than the product produced at225° C. (Ex. 8, 168 minutes). Similar trends were observed for lubeproducts from 2-MN (Ex. 9 to 12). For example, by running the reactionat a lower reaction temperature, such as 150 and 175° C. (Ex. 9 and 10),lube products with RBOT time of >1000 minutes were obtained. TABLE 2Effect of Reaction Temperature on Lube Yields and Properties from 1-MNand 2-MN Example No. 6 7 8 9 10 11 12 Feed, MN 1-MN 1-MN 1-MN 2-MN 2-MN2-MN 2-MN Olefin C16 1-C16 C16 C16 C16 1-C16 C16 Mole Ratio MN/O 2/1 2/12/1 2/1 2/1 2/1 2/1 Catalyst Type USY USY USY USY USY USY USY CatalystWt % 5 5 5 5 5 5 5 Rxn Temp, ° C. 175 200 225 150 175 200 225 Rxn Time,Hrs 8 4 3 72 8 4 2 % Total Conv. 49.2 71.3 79.8 63.9 67.3 70.8 69.7 %1-C16 Conv. 73.8 95.9 99.9 75.8 92.6 98.7 94.3 Product SelectivityMono-C16-MN 98.6 94.1 99.2 98.1 100.0 98.0 99.0 di-C16-MN 1.4 2.8 0.81.9 0.0 1.2 1.0 Others 0.0 3.1 0.0 0.0 0.0 0.8 0.0 Product Properties Kv@ 100° C., cS 5.5 5.6 5.6 5.3 5.3 5.3 5.3 Kv @ 40° C., cS 37.8 41.0 40.635.4 36.4 36.2 37.2 VI 72 62 62 73 68 64 59 Pour Point, ° C. −43 −46 −46−45 −49 −48 −49 Bro-mine No. 0.48 0.5 0.28 0.19 0.14 0 0.1 OxidativeStability RBOT, min 737 703 168 1111 1280 847 600 B10 Test at 163° C./40hrs % Kv Increase 0 6.5 13.8 7.2 6.5 9.2 9.9 TAN Incr., mg 0.4 1.6 2.050.5 0.49 1.2 1.63 KOH Sludge trace nil trace trace trace trace trace wt% lead loss 12.67 7.2 14.396 7.0 6.59 8.1 9.0

[0080] The data in Table 3 demonstrates the effect of different olefins,different MN sources and different catalysts on lube yields andproperties.

[0081] Examples 13 to 15 showed that 1-tetradecene, 1-hexadecene and1-octadecene may be used as the alkylating reagent. By changing theolefin feeds, lube products of 4.6 to 6.1 cS were obtained. All of theproducts possessed very long RBOT times (from 744 minutes to 1000minutes).

[0082] Examples 16 to 18 illustrate that different sources ofmethylnaphthalenes or a mixture of naphthalene and methylnaphthalenescan be used to produce high quality lube products. Suresol-187 used inEx. 16 and 17 is a commercial product available from Koch Chemical Co.and contains 52% 2-MN and 45% 1-MN. Example 18 used a feed containingequal weight of naphthalene, 1-MN and 2-MN. Again, the products ofexamples 16 to 18 were produced in high yields and had long RBOT time.

[0083] Example 19 and 20 demonstrate that using a MCM-22 catalyst,instead of a USY catalyst, produced lube products with excellent RBOTtime. TABLE 3 Effect of Different olefins, different MN sources anddifferent catalysts on lube yields and properties. Different OlefinsDifferent MN Source Different Catalyst Example No. 13 14 15 16 17 18 1920 Feed, MN 2-MN 2-MN 2-MN Suresol- Suresol- N, 1- 1-MN 2-MN 187 1872-MN Olefin C14 1-C16 C18 1-C16 1-C13 C16 1-C16 1-C16 Mole Ratio MN/O2/1 2.0/1 2/1 2.0/1 2.0/1 2/1 2.0/1 2.0/1 Catalyst Type USY USY USY USYUSY USY MCM22/ MCM22/ Al₂O₃ Al₂O₃ Catalyst Wt % 5 5 5 5 5 5 5 5 RxnTemp, ° C. 200 200 200 200 200 200 200 200 Rxn Time, Hrs 4 18 4 4 5 4 1818 % Total Conv. 76.0 77.9 80.5 71.5 68.6 90.5 59.3 75.1 % 1-C16 Conv.99.4 97.7 99.5 98.7 99.7 90.8 89.3 98.1 Product Selectivity Mono-C16-MN99.2 99.7 98.4 96.8 99.1 92.0 88.4 81.4 di-C16-MN 0.8 0.3 1.6 1.8 0.98.0 11.4 18.5 Others 0.0 0.0 0.0 1.4 0.0 0.0 0.2 0.1 Product PropertiesKv @ 100° C., cS 4.6 5.3 6.1 5.5 4.7 5.3 6.7 6.5 Kv @ 40° C., cS 30.836.8 43.3 38.1 32.0 35.5 53.0 51.1 VI 29 64 81 66 33 73 71 64 PourPoint, ° C. −46 −49 −26 −47 −48 −48 −45 −47 Bromine No. 0.08 0.03 0.12 00 0.21 0.62 0 Oxidative Stability RBOT, min 1000 744 817 216 170 191 121525 B10 Test at 163° C./40 hrs % Kv Increase 8.6 10.2 9.7 20.5 21.7 24.47.3 5.8 TAN Incr., mg 0.77 1.1 0.74 2.6 1.7 1.26 0.94 0.9 KOH Sludgetrace trace trace light trace trace nil trace wt % lead loss 8.056 8.68.904 16.5 15.8 13.911 8.4 3.7

[0084] Table 4 compares the lube properties made from 1-MN or 2-MNversus a commercial mono-alkylated naphthalene lube available from MobilChemical Co. (produced according to the method disclosed in U.S. Pat.No. 5,034,563). The data demonstrates that MN-based lube products havebetter oxidative stability as measured by the RBOT times. TABLE 4Comparison of Lube properties Made from MN vs. from Naphthalene AlkylNaphthalene Example No. 7 11 20 From Mobil Chem Feed, MN 1-MN 2-MN 2-MNNaphthalene Olefin 1-C16 1-C16 1-C16 1-C16 Product Properties Kv @ 100°C., cS 5.6 5.3 6.5 4.8 Kv @ 40° C., cS 41.0 36.2 51.1 27 VI 62 64 64 76Pour Point, ° C. −46 −48 −47 −43 Bromine No. 0.5 0 0 0.2 OxidativeStability RBOT, min 703 847 525 150 Oxidative Stability % Kv Increase6.5 9.2 5.8 7.6 TAN Incr., mg KOH 1.6 1.2 0.9 0.7 Sludge nil trace traceTrace wt % lead loss 7.2 8.1 3.7 9.9

[0085] Although the invention has been described in detail and withreference to specific embodiments thereof, it will be apparent to oneskilled in the art that various changes and modifications can be madetherein without departing from the scope and spirit of the presentinvention.

What is claimed is:
 1. A method for improving the oxidative stability ofa lubricant having an RBOT of ≦ about 200 minutes comprising adding tosaid lubricant a base oil comprising a compound of formula (I):

wherein R¹ and R² are H, methyl, ethyl, propyl, or butyl; R³ and R⁴ arean alkyl group having from about 6 to about 24 carbon atoms; x is from 0to about 2; and y is from 0 to about 4; with the proviso that at leastone of R¹ and R² is other than H, and at least one of x and y is otherthan 0; and wherein the base oil has a RBOT value of greater than about200 minutes.
 2. The method of claim 1, wherein said base oil comprisesat least 20 wt % of a compound of formula (I) or mixtures thereof. 3.The method of claim 1, wherein said base oil comprises at least 50 wt %of a compound of formula (I) or mixtures thereof.
 4. The method of claim1, wherein said lubricant comprises at least 2 wt % of said base oil. 5.The method of claim 1, wherein R¹ is H and R² is methyl.
 6. The methodof claim 1, wherein R² is H and R¹ is methyl.
 7. The method of claim 1,wherein the sum of x and y is one, R¹ is H and R² is methyl.
 8. Themethod of claim 1, wherein the sum of x and y is one, R¹ is methyl andR² is H.
 9. The method claim 1, wherein the sum of x and y is one. 10.The method of claim 1, wherein the sum of x and y is greater than
 1. 11.The method of claim 1, wherein said base oil has an RBOT value of about500 to about 1500 minutes.
 12. The method of claim 5, wherein said baseoil has an RBOT value of about 500 to about 1500 minutes.
 13. Asynthetic base oil comprising a mixture of monoalkylated andpolyalkylated naphthalenes wherein the improvement comprises saidsynthetic base oil containing at least 20 wt % of an alkylatednaphthalene selected from the group consisting of a compound or mixtureof compounds of the following formula (I):

wherein R¹ and R² are H, methyl, ethyl, n-propyl, n-butyl, or t-butyl;R³ and R⁴ are an alkyl group having from about 6 to about 24 carbonatoms; x is from 0 to about 2; and y is from 0 to about 4; with theproviso that at least one of R¹ and R² is other than H, and at least oneof x and y is other than
 0. 14. The synthetic base oil of 13 wherein atleast one of R¹ and R² is hydrogen.
 15. The synthetic base oil of claim14 wherein at least one of R¹ and R² is methyl.